The present invention relates to a method and apparatus for minimizing calcification of a heart valve.
The build up of calcified deposits on the superior surface of the aortic heart valve accounts for a large number of aortic stenosis cases. This condition is characterised by the build up of calcified nodules on the upper and superior surface of the valve leaflets. These nodules decrease the flexibility of the leaflets, thereby limiting their mobility and capacity to fully open to permit adequate blood flow.
One technique to correct aortic stenosis is valve replacement.
Heart valve replacement operations have been carried out for several years, on patients having degenerating heart valves.
A number of types of replacement heart valves are known, including porcine and non-porcine artificial valves.
Replacement heart valves made from treated tissue, such as pig valves, may also become less flexible and lose their effectiveness due to calcification, i.e. the build-up of calcified deposits on the surface of the aortic heart valves. This build up again limits the mobility of the valve leaflets and their capacity to fully open to permit adequate blood flow.
Accordingly, it is important to monitor the condition of implanted artificial heart valves. Early calcification can be a life-threatening complication which must be recognised promptly and treated by emergency valve replacement.
Furthermore, in some patients, valve replacement is not a viable option. For valve replacement to be possible, the patient must be healthy enough to undergo open heart surgery. Further, a patient receiving a replacement valve typically must take anticoagulation drugs for the rest of his or her life. Also, some patients have an aortic root that is not large enough to easily accommodate conventional replacement valves. For such patients, it is also important to monitor the aortic valve which may be susceptible to the build up of calcified deposits and to minimise the calcification, where possible.
U.S. Pat. No. 4,769,032 by Steinberg teaches a prosthetic valve and monitoring system which replaces the need for an echocardiogram by allowing the recipient to monitor his own valve continuously at home, or periodically in a Doctor""s office or a clinic etc. An artificial heart valve is provided with means for generating a detectable electrical current upon motion of the valve leaflets responsive to blood flow therethrough. The current signal can then be analysed to determine the condition of the leaflet. The leaflets of the artificial heart valve may be impregnated with magnetizing ions prior to implantation of the valve into the heart. Thereafter, blood flow through the heart valve opens the ion-impregnated heart leaflets. The motion of the leaflets induces a voltage in a solenoid coil opposed to the valve. The voltage varies in accordance with the velocity at which the valve leaflets open.
Many methods of treating artificial valves prior to implantation, to inhibit calcification after implantation, are known. Examples of such methods are disclosed, for example, in U.S. Pat. No. 5,051,401; U.S. Pat. No. 4,323,358; U.S. Pat. No. 4,378,224; U.S. Pat. No. 4,553,974; U.S. Pat. No. 4,648,881 and U.S. Pat. No. 5,002,566. In the latter of these, calcification-resistant bioprosthectic implants are made from tanned biological materials, e.g. porcine heart valves, bovine pericardium, human dura mater, etc which has been impregnated with a calcification-mitigating effective amount of a ferric and/or stannic salt. The impregnated biological materials and processes are particularly advantageous for the preparation of bioprosthetic heart valves. These implants have been planned to be highly resistant to calcification, in vivo.
It would be desirable to provide a system for treating a valve, particularly an artificial valve after implantation, in vivo.
U.S. Pat. No. 5,443,446 teaches a method and apparatus for in vivo heart valve decalcification. The apparatus for mechanical in vivo removal of calcified deposits from the valve includes an anchoring balloon catheter fixable across the valve, a tool for removing the deposit, and a mechanism for securing the tool with respect to the anchoring balloon and the aortic valve. A number of position balloons can be selectively inflated and deflated to correctly position the deposit removal tool.
The above US patent, however, does not act to prevent or minimize the build up of calcium deposits in the first place, but merely removes calcified deposits which have built up.
According to the present invention, there is a provided a method and apparatus for minimizing or inhibiting the build up of calcified deposits on an aortic valve, in vivo.
According to a first aspect, there is provided a method of inhibiting build-up of calcified deposits on an aortic valve, comprising applying electrical energy to the heart in the region of the valve, during the refractory period of the heart.
According to a second aspect, there is provided an implantable apparatus for inhibiting the build-up of calcified deposits on an aortic valve comprising an implantable pulse generator; means for sensing depolarizations of the heart; means for applying electric energy generated by the implantable pulse generator, to the heart, and control means for controlling the delivery of the electric energy to the heart in dependance on the detected depolarizations; wherein said control means is adapted to cause electrical energy to be applied to the heart in the region of the aortic valve during refractory periods of the heart.
The present invention provides a method and apparatus for preventing, or at least mitigating the build up of calcium on the tissue valve by treating the tissue valve within the body, i.e. in vivo, with electrical signals. In particular, in the preferred embodiment, the present invention uses a bipolar electrode in the high right atrium to xe2x80x9cfocusxe2x80x9d the electrical current onto the tissue valve during the ventricular refractory period.